Dual tractor road grader with double arched center frame

ABSTRACT

A double arch center frame employs a depending center arch to mount by a ball and socket connection the leading end of a draw bar and yoke assembly. Bell cranks pivotably mounted to yoke plates borne by the arched center frame intermediate of the center arch and the rear arch have arms pivotably coupled to respective hydraulic lift cylinders disposed on opposite sides of the center frame and to a like member common to the bell cranks. A side shift hydraulic cylinder is pivotably connected at one end to one side of a subframe rotatably supporting a mold board assembly and at the other end to a link member intermediate of its pivot connections to a second arm of the bell crank members. The forward arched end of the center frame is articulated to a front single axle tractor for rotation about right angle, vertical and horizontal axes, and the rear arched end of the center frame is hinge connected to a rear single axle tractor for pivoting about a horizontal axis. Multiple hydraulic crab steering cylinders force angulation of the tandem wheel tractors relative to respective ends of the double arch center frame to move the unit selectively into laterally offset crab steering conditions for the dual tractors for soft ground grading. In a further embodiment, a cab is provided on the rear tractor. Also, the rear steering cylinder mounts are moved closer to the center of the cross bar and the king pin hinge joint brackets are advanced forward of the rear end of the center frame.

This application is a continuation-in-part of application Ser. No.25,155 filed Mar. 21, 1979, now U.S. Pat. No. 4,279,312.

FIELD OF THE INVENTION

This invention relates to excavation apparatus employed in earth ormaterial removal, and in particular, to a grader for performingintermediate surface contouring and finishing operation.

DESCRIPTION OF THE PRIOR ART

For several years, motor graders have been used as road maintenancemachines and as contour finishing machines on earth moving projects.Early graders were pulled by a prime mover such as a wheeled ortrack-type tractor unit. The development of these machines has led toself-profelled models of increasing size horsepower. Most machinesavailable today are driven by rear wheels, the front wheels being mainlyemployed for steering. Some later models offer articulated rear jointsin addition to conventional steering axle. Such types of presentmachines are limited by the amount of power that can be transmitted bythe rear wheels. As a result of this, most manufacturers try toincorporate a decided weight bias on the rear wheels in an effort toobtain maximum traction. Because of the weight bias on the rear wheels,conventional motor graders have difficulty in operating in soft ground.Either rutting of the finished surface occurs or the unit itself becomesstuck in the soft ground. Such machines are also, upon occasion,difficult to steer because of blade loading, weight distribution and thelack of power driving the steering wheels. Attempts have been made tobuild motor graders that have all wheel drive, but these machines havenot been able to obtain the maneuverability and adequately position theblade at the same time.

In an effort to provide a motor grader to overcome the aforementionedproblem, there is disclosed a U.S. Pat. No. 3,568,778 a type of earthworking apparatus which comprises two similar mobile assembliesincluding drive engine and traction engine and which are reverselyoriented, supporting a main frame therebetween, in an articulatedsuspension with the main frame carrying a subframe which in turnrotatably supports the mold board and blade for effecting the scrapingof the surface being treated. The unit includes hydraulic cylinderoperated mechanisms for adjusting the angle of attack of the blade, theangular position of the blade with respect to the longitudinal centerline of the apparatus, and the tilt of the blade in the plane of itslongitudinal axis. Further, the structure of U.S. Pat. No. 3,568,778incorporates an operating cab which is mounted to the central or mainframe and which is rotatable about a vertical axis in an attempt to gainoptimum surveillance of the area of operation of the machine and tofacilitate controlled operation of the machine from this vantage point.

While the motor grader of U.S. Pat. No. 3,568,778 provides a machineoperating with improved precision and ease of handling, the apparatusitself is complicated in terms of proper positioning of the bladeassembly and forms a center frame of bifurcated frames pivoted at theiroutboard ends to the front and rear mobile assemblies about a verticalaxis and being pivotally coupled at their inboard ends to a centralframe. Hydraulic cylinders carried by each of the bifurcated frames acton extension members from the frame centered member to independentlyangularly orient respective ends of the central frame relative to thetransverse pivot axis for these members at the bifurcated ends of thebifurcated frames. This mechanism greatly increases the cost of themotor grader apparatus of U.S. Pat. No. 3,568,778 and renders thecentral frame assembly complex and unwieldly. It is, therefore, aprimary object of the present invention to provide an improved dualtractor motor grader apparatus which provides improved maneuverability,superior weight distribution for the load subjected to the apparatusduring earth grading, while simplifying the maneuverability andversatility in the positioning of the blade relative to the center framearticulated between the front end and rear end tractors.

Another object of the present invention is to provide a cab on the reartractor having controls therein for controlling the entire operation ofthe machine. In addition, the rear steering cylinder mounts are movedinwardly toward the center of their supporting cross beam and the upwardking pin hinge joint bracket members are advanced forwardly of the rearof the center frame.

It is a further object of the present invention to provide an improveddual tractor grader which provides improved, "crab" steering withoutinterferring with blade positioning both in terms of angle of attack andangular blade positioning relative to the longitudinal center line ofthe apparatus center frame, and which insures superior performance ofthe grader on conventional surfaces and vastly superior performance whenthe grader is operating on soft ground.

SUMMARY OF THE INVENTION

This invention relates to an earth working apparatus of the typedescribed in my co-pending application Ser. No. 25,155 filed Mar. 21,1979, now U.S. Pat. No. 4,279,312, of which this is a continuation inpart application. The invention employs a first single axle tractor anda second single axle tractor which are articulated to respective ends ofan arched center frame. A draw bar and yoke assembly including asubframe is mounted to the center frame, underlying the same, with thesubframe supporting a rotatable ring for rotation about an axisintersecting the plane of the draw bar and yoke assembly. A mold boardassembly including a mold board and blade is carried by the rotatablering for rotation with said ring. Means are provided for adjusting theangle of attack of the blade, the angle of inclination of the mold boardabout its longitudinal axis, the vertical lift position of the moldboard and blade and the lateral position of the rotatable ring andsubframe relative to the arched center frame. The improvement resides inthe arched center frame comprising a double arch member including adepending center arch intermediate of the depending arches at respectiveends. A ball and socket mount universally connects the leading end ofthe draw bar and yoke assembly to the center arch. Yoke plates fixed tothe center frame, intermediate of the center arch and the archarticulated to the second tractor, overlies the draw bar and yokeassembly and bears bell cranks pivotably mounted to the yoke means onrespective lateral sides of the center frame. The bell cranks includebifurcated arms with one arm pivotally coupled to one end of acorresponding hydraulic lift cylinder disposed on that side of thecenter frame and a second arm pivotably coupled to a link member commonto the bell cranks, with the apex of the bell cranks being pivotablymounted to the yoke means. Means are provided for pivotably connectingthe other end of the lift cylinders to the subframe on opposite sides ofthe center frame, and further means are provided for pivotallyconnecting a side shift hydraulic cylinder to said subframe at one sideof the center frame and the other end of the hydraulic cylinder to thelink member intermediate of its pivot connection to the second arms ofthe bell crank members. Extension and retraction of the hydraulic liftcylinders causes the subframe, the rotatable ring and the mold boardassembly to be vertically raised or lowered, extending or retracting oneof the hydraulic lift cylinders with respect to the other causes themold board assembly to be tilted in the plane of the longitudinal axisof the mold board, and extension or retraction of the side shifthydraulic cylinder causes the subframe and the mold board assembly to beshifted laterally with respect to the longitudinal center line of thecenter frame.

The first tractor may comprise a generally L-shaped trunior including avertical part at the rear of the first tractor and a horizontal partextending generally at right angles thereto and projecting rearwardly ofthe first part, said trunion being mounted to the first tractor forrotation about a general horizontal axis and including upper and lowerking pins for pivotally connecting one arch end of the center frame tothe trunion for rotation about a generally vertical axis. A first pairof hydraulic crab steering cylinders are pivotably connected at one endto the trunion horizontal part on opposite sides of the center frame andto the arched end of the center frame adjacent the king pin connectionpivot point between the center frame and the trunion. The oppositearched end of the center frame is hinge connected to the second tractorby a hinge joint permitting pivoting of the second tractor relative tothe center frame about a generally vertical axis. A second pair of crabsteering hydraulic cylinders are respectively pivotably connected atrespective ends to the center frame arched end adjacent the hinge jointon opposite sides thereof and to the second tractor means on oppositesides of the hinge joint connection between the second tractor means andthe center frame such that extension and retraction action of the crabsteering hydraulic cylinders effects angular orientation of the tractormeans with respect to the center frame at respective ends thereof tocause the first tractor and the second tractor to move into laterallyoffset positions with respect to each other for crab steering underclose control and insure fine grading by the blade regardless ofdirection of movement of the unit, angle of attack of the blade, angularposition of the mold board and blade relative to the longitudinal axisof the center frame supporting the same.

Preferably, a mold board support assembly is fixed to the ring anddepends therefrom and comprises laterally opposed support plates atright angles to the plane of the draw bar and yoke assembly. Mold boardpivot plates are pivotably connected to opposed support plates, to theside thereof, for pivoting about an axis generally coplanar to the planeof the draw bar and yoke assembly. At least one blade attack angleadjustment hydraulic cylinder is pivotably connected at one end to saidsubframe and at its opposite end to a mold board pivot plate remote fromthe pivot point of the pivot axis of the mold board pivot plate topermit variance in angle of attack of the blade by relative extensionand retraction action of the hydraulic cylinder. The mold board includesa pair of slide bars fixedly mounted thereto and slidably positionedwithin grooves provided along corresponding edges of said mold boardpivot plate to permit the mold board assembly to slide transversely ofthe mold board support assembly. Hydraulic mold board lateral shiftcylinder means is operatively mounted to the mold board assembly at oneend and to the slide bars at the other end such that extension andretraction action of the hydraulic mold board lateral shift cylindermeans causes the mold board and the scraper blade carried thereby to beshifted laterally relative to the axis of rotation of the ring memberand the center of the subframe.

A further embodiment of the present invention contemplates theelimination of operator controls on the front tractor and the provisionof a cab on the ear tractor from which the operator may control theentire operation of the machine and from which the operator may havetotal visibility over the movement of the mold board and blade.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of the improved dual tractor motorgrader apparatus of the present invention, in one form.

FIG. 2 is a top plan view of the grader of FIG. 1.

FIG. 3 is a top plan view of the draw bar and yoke assembly of theapparatus shown in FIGS. 1 and 2.

FIG. 4 is a vertical longitudinal sectional view of a portion of theapparatus of FIG. 3 taken about line IV--IV, showing the ring drivemechanism.

FIG. 5 is a vertical sectional view of a portion of the apparatus ofFIG. 1 taken about line V--V.

FIG. 6 is a top plan view of a portion of the apparatus of FIG. 1illustrating the mounting of the subframe to the center frame.

FIG. 7 is a vertical sectional view of a portion of the apparatus ofFIG. 1 taken about line VII--VII.

FIG. 8 is an enlarged vertical, longitudinal sectional view showing thearticulared joint between the center frame and the front tractor unit.

FIG. 9 is a top plan view of the apparatus of FIG. 1 in "crab" steeringposition.

FIG. 10 is a side elevational view of a modified form of the improveddual tractor motor grader apparatus of the present invention wherein thefront tractor controls have been eliminated and the rear tractor isprovided with a cab from which the operator controls the entireoperation of the apparatus.

FIG. 11 is a top plan view of the grader of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, the improved, dual tractor motor grader orapparatus is indicated generally at 10 and comprises principally a fronttractor unit indicated generally at 12, and oppositely oriented reartractor unit indicated generally at 14, a double arch center frameindicated generally at 16 and being articulated to said front tractorunit by way of articulated joint indicated generally at 18 and beinghinged for pivoting about a vertical axis through a vertical axis hingejoint indicated generally at 20. Further, the apparatus 10 furthercomprises, principally, a mold board assembly indicated generally at 22mounted to and supported by a subframe indicated generally at 24 by wayof a draw bar and yoke assembly indicated generally at 26 which isadjustably controlled by way of a blade positioning mechanism indicatedgenerally at 28.

The front tractor unit consists of a chassis 30 supported by single axleas at 32 to each side of the chassis 30 which bears a power source as at34. The unit may be driven and controlled from either of the tractors,but is here shown as being controlled by an operator seated upon thefront seat at 36 and controlling the steering of the vehicle through asteering wheel as at 38. The power source 34 may include a suitablediesel or gasoline internal combustion engine as is conventional. Theengines both for the front tractor unit 12 and the rear tractor unit 14operate suitable hydraulic pumps and motors to both drive the unitsunder positive traction and to control the various components in termsof their position and angular orientation as will be describedhereinafter.

The rear tractor 14 may be a twin to the front tractor unit 12 or thesetwo components may comprise the front and rear tractor units of aconventional tractor scraper such as a scraper under TEREX modeldesignation TS-14 manufactured by the General Motors Corporation.However, the nature and make up of the center frame 16, the mold boardassembly, its support and positioning and the articulation of the centerframe both to the front tractor unit and the rear tractor unit aredecidely different from the TEREX TS-14 dual tractor scraper. Thechassis 30 of the front tractor unit 12 supports a vertical steeringtrunion 40 including a vertical part 40a and rearwardly directedhorizontal post 40b, and which is L-shaped and mounted to chassis 30 forpivoting about a horizontal axis. Trunion 40 bears an upper king pin 42which pivotably mounts the leading end 16a of the center frame to thefront tractor unit for pivoting about a vertical axis, this pivot actingin conjunction with a lower king pin 21.

Referring to FIG. 8, the articulated joint 18 between the forward end orarch 16a of the center frame 16 and the front tractor unit 12 may bemore readily seen. In that respect, the forward end 16a of the centerframe 16 bears the lower king pin 21 which extends through a verticalhole 23 formed within a horizontal part 40b of the trunion 40 andprojects through a suitable vertical hole 25 within the lower portion ofthe front end 16a of the center frame 16. A suitable bearing plate orwasher 27 is interposed between the center frame 16 and the trunion 40.The part 40a of the trunion 40 is bifurcated and acts to pivotablysupport one end of a pair of hydraulic crab steering cylinders 44through their pin connections as at 44a via arms 46. The other end ofeach hydraulic cylinder 44 is pivotally connected to the forward arch16a, on opposite sides of the center frame 16. Further, the chassis 30is pivotably mounted to the trunion 40 through paired king pins 29 whichproject through drilled holes within yoke 31 and depending brackets 33carried by the trunion 40, such that trunion 40 and center frame 16, atthis point pivot about a horizontal axis. The wheels 32 are mounted tothe frame by way of springs 35 bearing axle 37.

Extension and retraction action of hydraulic cylinders 44 causes thecenter frame 16 to pivot about the axis of the king pins 21 and 42 so asto shift the rear tractor unit 14 as well as the elements carried by thecenter frame 16, to the right or left of the center longitudinal line ofthe front tractor unit 12.

The double arch center frame 16 is essentially an elongated M-shapedmember in vertical elevation terminating at its rear in a depending archor rear end 16b. The center frame 16 is of square hollow plateconstruction for providing a large strength to mass ratio. The rear end16b of the center frame 16 bears a series of horizontal bracket membersor plates for partially defining an upper king pin hinge joint as at 52and a lower king pin hinge joint 54. The joint 52 comprises pairedplates 56 and 58 which extend rearwardly and which are welded or thelike to the center frame 16 and which bear aligned holes through whichproject an upper king pin 60. The upper king pin 60 defines along withthe lower king pin 62, mounted between an upper plate 64 and a lowerplate 66, a vertical pivot axis 68 for the center frame relative to therear tractor unit 14. The tractor unit 14 bears single axle as at 32,which may be identical to those of the front tractor unit 12, mounted toa chassis 30 which bears its own power unit 34 including a diesel orinternal combustion engine. The chassis 34' is provided with upper andlower pin connecting bars as at 70 and 72, respectively, these barsbeing apertured and sized to receive the upper and lower king pins 60and 62. For controlled angular orientation about the vertical axis 68 ofthe rear tractor unit 14 with respect to the center frame 16 at its rearend 16b, the brackets or plates 52 and 56 pivotably couple as at 73 atone end the projecting rods 74 of respective left and right hydrauliccrab steering cylinders 76 whose opposite ends are pivotably connectedas at 78 to a transverse beam or cross bar 80 which spans across thefront end of the chassis 30' of the rear tractor unit 14. Thus, as thecylinders 76 are respectively operated hydraulically in retraction andexpansion, in an opposite sense, the rear tractor unit 14 is required toangulate about the vertical axis 68. Thus, by power application, thedual tractor grader may be forced into "crab" steering orientation,where the rear tractor unit 14 does not track the front tractor unit 12,but is laterally shifted with respect thereto so that the wheels 32 ofthe two units will not pass over the same ground. This is particularlyimportant where soft ground grading occurs.

As best seen in FIG. 7, the chassis 30' includes both an uppertransverse beam or cross bar 80, at the level of the upper king pin 60,and a corresponding lower transverse beam or cross bar 82 acting as amount for the bar 72 and being joined to the upper beam 80 by suitablevertical bars 84 which are welded at their upper and lower ends torespective beams 80 and 82 to define an open vertical framework. Thischassis, therefore, facilitates the hinge connection between the reartractor unit 14 and rear arch 16b of the center frame 16 with controlledangular orientation between these elements by extension and retractionof the hydraulic cylinders 76.

The draw bar and yoke assembly 26, FIGS. 1, 2, 3, comprises a bifurcateddraw bar 90 which opens outwardly in a rearward direction from itsforward end 90a which attaches by means of a draft bolt 92 bearing aball 92a to a central arch 16c of the double arch center frame 16 bymeans of a cap 94 which surrounds the ball of the draw bolt 92 to form aball and socket universal connection. The cap 92 is bolted to a plate 96of the central arch 16c of the center frame 16. The bifurcated draw bar90 is welded to a cross bar 98 at its open rear and which elements arein turn welded to or alternatively bolted to an underlying yoke 100, theyoke 100 and the bifurcated draw bar 90 forming the principal elementsof a subframe 99. The yoke 100 supports by bolts or other means a seriesof radially outwardly projecting, depending shoes 101, FIG. 5, in asemi-circular array which support a large metal ring or member 102,bearing teeth 104 on its inner periphery and defining an annular rack.The shoes support the ring 102 for rotation about its axis which extendsthrough the open center 106 of the yoke 100. A hydraulic ring drivemotor 108 is mounted to the upper face of yoke 100 in between thebifurcated portions of the draw bar 90 with the hydraulic motor 108connected to a driven pinion gear 110, FIG. 4, borne by a vertical axisgear transmission unit indicated generally at 112 and comprised of acylindrical casing 114 which is peripherally recessed at 114a on one endso as to fit within an opening 116 formed within the yoke 100. Thecasing 114 forms a large central sleeve bearing 118, supporting shaft120 for rotation about its axis. The shaft 120 bears pinion gear 110 atone end above the yoke 100 and bears below the yoke 100, a drive pinion122 which meshes with the annular rack 104 of ring 102. Operation of thehydraulic motor 108 acts to rotate the ring 102 a full 360° in eitherdirection about its axis supported by the shoes 101. The function ofring 102 is to support the mold board assembly indicated generally at 22for rotation about the ring axis.

Further, due to the ball and socket connection of the forward end of thedraw bar 90, the subframe 99 is lifted vertically as well as tiltedabout the horizontal longitudinal center line of the center frame 16,while additionally, the subframe 99 and the components carried therebyincluding the mold board may be shifted sidewise relative to thatlongitudinal center line.

Referring next to FIG. 5, it may be seen that the double arch centerframe 16 which preferably takes the form of a hollow rectangle hasrigidly fixed thereto by way of welding or the like a pair oflongitudinally spaced yoke or collar plates 124, FIGS. 5, 6, abovesubframe 99, the plates 124 mounting paired pivot pins 126 to respectivesides of the center frame 16. Left and right bell cranks or members 128and 130 are pivotably mounted at the apex of their arms 128a, 128b and130a, 130b by way of the pins 126 to the yoke or collar plates 124, thebell cranks being V-shaped in configuration. The arms 128b and 130b arepin connected by way of pins 132 to a common link or member 134 whichspans beneath the center frame 16. The bell crank member arms at 128aand 130a are double pivotably mounted by way of yokes 136 to left andright lift cylinders 138 and 140. The hydraulic lift cylinders 138 and140 are mounted so that they may pivot about intersecting horizontalaxes as defined by pins 142 which are born within bosses 138 at theouter ends of the bell crank arms 128b and 130and by pins 143 of theyokes 136. Further, the left cylinders 138 and 140 are provided withextendable and retractable rods 138a and 140a, respectively, which arepivotably connected to the subframe cross bar 98 by way of ball andsocket connections through bosses 146 which project to one side of thecross bar 98 of the subframe 99. The bell crank members 128 and 130 actdue to their connection by way of link 134 to facilitate the tilting ofthe subframe 99 and the mold board assembly 22 carried thereby about thelongitudinal center line as defined by the center frame 16 between thefront and rear tractor units regardless of whether these units are inturn longitudinally aligned or laterally offset and in a "crab" steeringorientation.

Additionally, and very important to the present invention, is theconnection between the subframe cross bar 98 and one end of a hydraulicblade side shift cylinder 148. A ball and socket connection 148a iseffected at boss 150, FIG. 3, borne by cross bar 98 while rod 149 ofthat hydraulic cylinder 148 is pivotably connected to link 134intermediate of its pivotable connections to the bell cranks 128 and130. Extension and retraction action of rod 149 shifts the subframe 99and all elements carried thereby laterally to the left or right relativeto the center frame.

Turning next to the mold board assembly 22, the present inventionfeatures a mold board assembly wherein the mold board itself as at 170bearing blade 171 is laterally shiftable with respect to the center ofthe mold board support assembly indicated at 156 which rigidly connectsto ring member 102 so as to rotate therewith. In this respect, welded orotherwise affixed to opposite mold board sides of ring member 102 aremodified inverted L-shaped support plates 158 which extend forwardly,and which are fixed to opposite ends of cross beam or cross bar 174.Diagonal reinforcing members 160 meet at a flat plate 162 to which theyare welded at their inner ends with the plate being welded to the ringmember. The opposite ends of the diagonal members 160 are fixed torespective plates 158 to define along with a lower cross beam or bar 175and a pair of vertical intermediate support bars 177, the open framework mold board support assembly 156. Further, this mold board supportassembly 156 bears a hydraulic mold board lateral shift cylinderindicated at 179 which spans across the frame work beneath the ringmember 102 and which carries an extensible and retractable rod 181. Therod 181 is fixed at its outboard end, by way of cross bar 183, to a pairof slide bars 164 which are parallel to each other and which areslidably mounted within notches or recesses 182 within edges ofangularly adjustable mold board pivot plates 176. The mold board pivotplates 76 are pivoted at their lower ends by way of pivot pins 172 tosupport plates 158. Plates 176 include arcuate slots as at 185 throughwhich project a threaded bolt 187 having one end fixed to the adjacentplate 158 and bear nuts 180 on their opposite end such that oncepositioned, by torquing the nuts 180, the arcuate position of the moldboard 170 may be secured providing a desired blade tip attack angle toblade 171. The mold board 170 is fixed to the slide bars 164 so as toslide therewith, permitting the mold board and the blade to be shiftedlaterally relative to the axis of rotation of the mold board supportassembly 156 and the ring member 102. Arcuate positioning and variationin the angle of attack of the blade 171 is effected by means of bladetip angle control hydraulic cylinders 178 mounted to each side of themold board support assembly 156.

Specifically, one end of each cylinder 179 is pivotably connected to thecross bar 174 outboard of its plate 158, while the projecting end of thecylinder rod 178a is pivotably connected to its pivot plate 175 remotefrom the pivot axis of that plate.

The hydraulic lines leading to and from the double action hydrauliccylinders have purposely been eliminated from the drawings to moreclearly show the hydraulic cylinders and the mechanisms they control.However, the gasoline or diesel engine power source for providing thepower necessary to propel the grader and to effect change in orientationand positioning of the various elements includes a source of hydraulicfluid, a pump and the controls for the hydraulic cylinders, all of whichare fully conventional and preferably located within the front tractor12 although this could optionally be on the rear unit with suitable partreversal. However, duplicate internal combustion engine power meanspump, hydraulic fluid source and controls may be provided to the reartractor unit 14 including a steering mechanism such that the unit may bedriven forwards or backwards, at will, without the necessity formovement of the grader relative to the earth formation being workedother than orientation of blade 171.

Further, since the mold board assembly 22 can be rotated a full 360°,the blade angle of attack may be readily varied, the side inclination ortilt of the blade may be changed, the mold board and blade itself may beshifted transversely through the axis of rotation defined by the ring102, it is evident that the machine is simply constructed but highlyversatile. In operation, power may be supplied by either or both of thepower tractor units 12 or 14. Because of the articulated joint 18, thecenter frame 16 may be inclined relative to the vertical plane of thefront tractor unit, and the center frame may be pivoted by energizationof hydraulic cylinders 44 and/or 76, FIG. 9, which will have the effectof causing the tractor units or the mold board assembly 22 and tractorunits to be shifted transversely to the right or left relative to eachother. By operation of the hydraulic cylinders 44 and 76, the centerframe may be pivoted relative to the longitudinal axis of the front andrear tractor units. This may be achieved without change of either theangle of attack of the blade 171 (and the mold board 170), the angle ofinclination of the mold board assembly 22 transversely through the axisof rotation of ring 102, the angular position of the mold board andblade by rotation of the ring 102 about its axis or the lateral positionof the mold board and the blade by operation of hydraulic cylinder 179.Extremely close control in the maintenance of attitude of the mold boardassembly and the blade is achieved as well as superior positioning ofthe tractor units, particularly where they are laterally offset or in"crab" steering orientation.

A further embodiment of the invention is shown in FIGS. 10 and 11wherein the front engine 12' replaces the front tractor 12 and thedouble arch center frame 16 is articulated to the front engine by way ofan articulated joint 18. The opposite end of the frame 16 is pivotableto the rear tractor 14 about a vertical axis through a vertical axishinged joint 20.

The articulated joint 18 is identical to that shown in FIGS. 1, 2 and 8and no additional description is deemed necessary to an understanding ofthis embodiment.

The mounting plates 200 and 202 for the steering cylinders 76 aresecured to the cross bar 80 inward of the ends 204. The positioning ofthe mounting brackets 202 and 204 inward toward the center of the bar 80will require the repositioning of the bracket plates 56 and 58 forwardof the rear 206 of rear end 16b. This is accomplished by extending orenlarging plates 56 and 58 to a point near the inner end 208 of the rearend 16b. Repositioning of the cylinder mounts, cylinders and cylinderbracket plates in this fashion is advantangeous in that the operatorwill have better visibility of the mold board 170 and blade 171 whenthey are angled backward in the extreme position.

To further aid in providing better visibility for the operator, a cap210 is provided on the rear tractor 14. The cap 210 has rear verticalposts 212 (one shown) which are supported on a downwardly inclined beam214. Front forwardly inclined vertical posts 216 (one shown) are securedto plates 218 supported on the ends 220 of the beam 214. The front andrear posts are spaced apart by horizontal bars or beams 222 and 224 (oneeach shown). A suitable opening or door 226 provides access to the caband a front window 227 is pivotable outwardly so as to permit additionalair to enter the cab. Controls for the front engine, rear tractor andsteering mechanisms are arranged within the cab whereby the operator maycontrol the operation of the apparatus with the greatest possible easeand visibility.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What I claim is:
 1. An earth working apparatus comprising:a single axleengine means, a single axle tractor means, a double arched center framearticulated at one end thereof to said engine means and at the other endthereof to said tractor means, a draw bar and yoke assembly including asubframe mounted to said center frame, said subframe supporting arotatable subframe ring for rotation about an axis intersecting theplane of said draw bar and yoke assembly, a mold board assemblyincluding a mold board and blade carried by said rotatable ring andmeans for adjusting the angle of attack of said blade, the angle ofinclination of the longitudinal axis of said mold board, the verticallift position of the mold board and blade, and lateral position of themold board and blade, and lateral position of the rotatable subframering relative to the arched center frame, the improvement wherein: saiddouble arched center frame comprising a first arcuate underportion, asecond arcuate underportion spaced longitudinally from said firstarcuate underportion, said first arcuate underportion including a firstdepending leg and a second depending leg, said second arcuateunderportion including a third depending leg and a fourth depending leg,said second depending leg and said third depending leg definingtherebetween a depending center common leg of said double arched centerframe, a ball and socket mount connecting the leading end of said drawbar and the yoke assembly to said depending center common leg of saiddouble arched center frame. a pair of longitudinally spaced yoke platesaffixed to said center frame intermediate of said center common leg andsaid other end of said arched center frame, bell cranks pivotablymounted to said spaced yoke plates on respective lateral sides of saidcenter frame and each including a first arm doubly pivotably coupled toone end of a corresponding hydraulic lift cylinder for pivotal movementabout intersecting horizontal axes, each lift cylinder disposed on arespective side of said center frame and a second arm at an angle tosaid first arm and pivotably coupled to a link member common to saidbell cranks, means for pivotably connecting the other end of said liftcylinders to said rotatable subframe ring on opposite sides of saidcenter frame, means for pivotably connecting one end of a side shifthydraulic cylinder to said subframe at one side of said center frame andat the other end to said link member intermediate of its pivotconnections to the second arms of said bell crank members, such thatextension and retraction action of said hydraulic lift cylinders causessaid subframe, said rotatable ring and said mold board assembly to bevertically raised or lowered, extending or retracting one of saidhydraulic lift cylinders with respect to the other, causes said moldboard assembly to be tilted in the plane of the longitudinal axis of themold board and extension or retraction action of said side shifthydraulic cylinder causes said subframe and said mold board assembly tobe shifted laterally with respect to the longitudinal center line ofsaid center frame, a first pair of hydraulic crab steering cylinders arerespectively pivotably connected to the single axle engine means and tothe arched end of said center frame, a second pair of hydraulic crabsteering cylinders are respectively pivotably connected at respectiveends to said center frame arched end adjacent the inner end thereof andto the tractor means toward the center thereof such that extension andretraction action of said hydraulic crab steering cylinders effectsangular orientation of said engine and said tractor means with respectto said center frame at respective ends thereof to cause said enginemeans and said tractor means to move into laterally offset position withrespect to each other and into crab steering position, and a cabsupported on inclined beams on said tractor means whereby an operatormay control the operation of the apparatus and view the mold board andblade when they are angled backward in the extreme position.